With the increasing need for the transfer of data over large distances, and the increasing use of Ethernet networks for local area networks (LANs), there has arisen a need for greater connectivity between LANs which provide greater data transfer rates and lower overhead, i.e. processing operations, for connecting LANs. In the prior art, devices known as bridges, routers, and gateways are available and well known for connecting LANs such as Ethernet segments over wide area networks (WANs). However, these prior art devices all have shortcomings. For example, bridges generally connect two Ethernet segments and are frequently limited to relatively short distances there between. While gateways and routers offer greater connectivity of Ethernet segments, these systems utilize network or transport level protocols to route data cells over LANs to their intended destination and must explicitly copy data cells destined for multiple destinations, as is required in broadcast application. Therefore, these prior art devices have limited usefulness and applicability.
In order to solve these and other problems in the prior art, the inventors herein have succeeded in designing and developing an ATM-Ethernet portal which conveniently connects disjoint Ethernet segments over an ATM/BISDN network (Asynchronous Transfer Mode/Broadband Integrated Services Digital Network), creating one large logical Ethernet segment. The portal of the present invention utilizes the ATM network transparently, with low overhead, and at speeds which exceed those of Ethernet segments such that operator usability and data transfer rates are non-limited. Each Ethernet frame transmitted on any one of the Ethernet segments is fragmented into a sequence of ATM cells, which are then transmitted by the local portal over the ATM network and delivered to the interconnected portals. When ATM cells are received at a portal, the cells are reassembled into Ethernet frames for transmission over their local Ethernet segments. The high level protocols used by the Ethernet hosts (that is, those protocols located above the data link layer in the ISO-OSI model) are not interpreted by the portal or by the ATM network. This contributes to the low overhead of the portal.
One of the significant advantages of the portal of the present invention is that it utilizes a dual port memory and a DMA transfer controller for moving either Ethernet or ATM data directly into this shared memory where header data is appropriately associated or disassociated therewith, and then out again to its destination under control of a microprocessor. With this hardware and methodology, the need to copy data cells is eliminated thereby dramatically decreasing the processing required by the portal and increasing the data throughput rate. As mentioned above, the rapid data throughput rate of the portal renders the ATM network connection transparent between Ethernet segments which may be separated by large distances. Of course this is a highly desirable feature and, in some applications, a requirement for the ATM network connection to be a useful interconnection scheme.
The hardware implementations of the present invention may be configured in either one of two contemplated arrangements as presently considered by the inventors herein. The first of these is a "standalone" implementation where all of the components are integrated on one or more custom design circuit boards to provide a custom portal device. Secondly, an "off the shelf" implementation may be utilized where the commonly available subsystems are comprised of purchased parts which are then integrated with a custom design ATM cell processor. This results in essentially a "PC" version which may be implemented through a commercially available PC with extra hardware added. The inventors have chosen the "off the shelf" strategy in implementing a prototype. However, for cost and size reduction, the "standalone" implementation would perhaps be more desirable in some applications.
With only minor modifications, the portal of the present invention may be extended to function as an ATM-Ethernet concentrator. As a concentrator, the device will multiplex a plurality of Ethernet controllers, each of which is associated with its own Ethernet segment, and provide connectivity between the plurality of Ethernet controllers and other Ethernet controllers/segments through an ATM network. Essentially, instead of a single Ethernet controller as is found in the portal, a common bus interconnects a plurality of Ethernet controllers to the concentrator which multiplexes their output and demultiplexes data being input. For larger concentrators for use with more Ethernet controllers, a wider bus and faster control microprocessor are utilized. The concentrator of the present invention, as with the portal, permits a transparent interconnection between local and remote Ethernet controllers/segments, and its operation is enhanced through the use of a dual port shared memory, DMA controller, and control microprocessor as is included in the portal design.
While the principal advantages and features of the present invention have been described above, a more complete and thorough understanding of the invention may be attained by referring to the drawings and description of the preferred embodiment which follow.